System for removing contaminants from plastic resin

ABSTRACT

A resin recycling system that produces essentially contaminant-free synthetic resin material in an environmentally safe and economical manner. The system includes receiving the resin in container form. A grinder grinds the containers into resin particles. The particles are exposed to a solvent in one or more solvent wash vessels, the solvent contacting the resin particles and substantially removing contaminants on the resin particles. A separator is used to separate the resin particles and the solvent. The resin particles are then placed in solvent removing element where they are exposed to a solvent removing agent which removes any residual solvent remaining on the resin particles after separation.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part (CIP) of U.S. patentapplication Ser. No. 11/096,880, filed Apr. 1, 2005, which isincorporated by reference.

GOVERNMENT SPONSORED DEVELOPMENT

The U.S. Government has rights in this invention pursuant to contractnumber DE-ACO4-01AL66850 with the United States Department of Energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improved system for removingcontaminants from synthetic resin materials, such as plastic. Moreparticularly, the present invention relates a resin recycling systemthat produces essentially contaminant-free synthetic resin material inan environmentally safe and economical manner.

2. Description of the Prior Art

Recycling containers made from synthetic resin material is a highlydesirable alternative to landfilling such containers. However, thesecontainers often include residues of the material they once contained.These residues if not removed can decrease the value of the containermaterial making it suitable for only low-grade products. Traditionally,these residues or contaminants have been difficult and expensive toremove and prone to create additional waste byproducts.

Recycling of motor oil containers is illustrative of the problem. Motoroil containers typically are high-density polyethylene (HDPE) whichlends itself well to recycling if it is sufficiently clean. However,residual oil coating the interior surface of the “empty” motor oilcontainers constitutes a contaminant that prevents re-use of thecontainers in at least a high grade plastic application, such as thepackaging of food or beverages.

The aforementioned problem is not just limited to oil containers.Similar contamination problems exist for example with pesticides fromHDPE containers, milk from HDPE containers, “soda water” frompolyethylene terephthalate (PET) containers, polychlorinated biphenyl(PCB) contaminants particularly from automotive plastics, andcontaminants from various other post-consumer containers, such asdetergent containers, collected from curbside recycling programs.

The significant amount of the above mentioned types of containers arecurrently disposed of in landfills, leaking oil and other contaminantsinto the soil and groundwater, and occupying significant landfillvolume.

Several known options exist other than landfilling the waste syntheticresin containers, including (a) grinding the containers and using themin other recycling processes on a very limited (dilute) basis; (b) usingan aqueous process to displace the contaminant from the synthetic resinmaterial; (c) using a halogenated solvent to dissolve/dilute thecontaminant; or (d) using a combustible or flammable solvent todissolve/dilute the contaminant oil from the synthetic resin material.

The problems with these options are as follows:

Existing recyclers in the United States can blend limited quantities ofcontaminated synthetic resin materials in recycled products. Largequantities cannot be blended because of the undesirable effects of thecontaminants on the recycled synthetic resin material properties.Examples include “plastic lumber” and lower grade plastic products.

Aqueous processes can be used to displace the contaminants from thesynthetic resin material. However, detergents and/or surfactants arerequired to assist displacement of the contaminants. A stream of usablecontaminant-free synthetic resin material will be generated by thismethod; however, the displaced contaminants will need additionalprocessing to separate them from the aqueous solutions or dispersions.The aqueous solutions or dispersions themselves will be a secondarywaste stream that will require treatment before being recycled ordischarged as waste water.

Halogenated solvents can be used to dissolve/dilute the contaminantsfrom the synthetic resin material. Again, usable synthetic resinmaterial will be obtained by this process if the solvents do not extractessential components from the synthetic resin material. The halogenatedsolvent solutions will require distillation to recover the contaminantsand recycle the solvents. In general, it is difficult to fully reclaimusable contaminants (such as oil) from the distillate. Furthermore, manyhalogenated solvents are ozone depleting compounds and potential healthhazards to humans, and therefore their use and release into theenvironment are under regulation and close scrutiny by federal and stategovernments.

Combustible or flammable solvents may be used to dissolve and/ordisplace the contaminants from the synthetic resin material. Usablesynthetic resin material can be generated by this method if the solventsdo not extract essential components from the synthetic resin material.The combustible or flammable solvent solutions will require distillationto recover the contaminants and recycle the solvents. Only distillationequipment suitable for combustible or flammable solvents may be used andeven then fire safety concerns will be significant. As in the case ofthe use of halogenated solvents, the contaminant may not be fullyrecoverable from the distillation.

Accordingly, there is a need for an improved system and method forremoving contaminants from synthetic resin material containers. Moreparticularly, there is a need for a system and method that will produceessentially contaminant-free synthetic resin material in anenvironmentally safe and economical manner.

SUMMARY OF THE INVENTION

The present invention solves the above-described problems and isdirected to a resin recycling system that produces essentiallycontaminant-free synthetic resin material in an environmentally safe andeconomical manner. The system includes receiving the resin typically incontainer form. A grinder is used to ground the received containers intoresin particles. One or more solvent wash vessels are provided toexposed the particles in a solvent. In the vessels, the solvent contactsthe resin particles and substantially removes the contaminants. Aseparator is provided to separate the particles and the resin afterremoval from the one or more vessels. Thereafter, the resin particlesare introduced into an extraction vessel where the particles are exposedto a solvent removing agent, which substantially removes any residualsolvent remaining on the resin particles after separation. In variousembodiments of the invention, the resin may be received in the form ofbales of compacted containers. The containers may also be initiallysorted by color before grinding. The solvent may be an organic solvent.The solvent removing agent is either a liquid or supercritical carbon.In yet another embodiment, the contamination-free particles areseparated by type, such as HDPE or PET, after the particles are exposedto the solvent removing agent. These and other important aspects of thepresent invention are described more fully in the detailed descriptionbelow.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A preferred embodiment of the present invention is described in detailbelow with reference to the attached drawing figures, wherein:

FIG. 1 is a schematic flow diagram depicting a three-stage solventsystem and a liquid or supercritical carbon dioxide system for removingcontaminants from particulate synthetic resin material.

FIG. 2 is a detailed view of the three-stage solvent system shown inFIG. 1.

FIG. 3 is a diagram illustrating a resin recycling method and apparatusaccording to the present invention.

Like reference numbers in the figures refer to like elements.

The drawing figures do not limit the present invention to the specificembodiments disclosed and described herein. The drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawing figures, and particularly FIG. 1, a processfor removing contaminants from post-consumer containers made fromsynthetic resin material in accordance with a preferred embodiment ofthe invention is illustrated. The present invention is particularlyuseful in the removal of oil from high density polyethylene containers,pesticides from HDPE containers, milk from HDPE containers, “soda water”from polyethylene terephthalate containers, polychlorinated biphenyl(PCB) contaminants particularly from automotive plastics, andcontaminants from various other post-consumer containers, such asdetergent containers, collected from curbside recycling programs. Also,the present system is highly effective in removing labels and labeladhesive from synthetic resin material containers. Furthermore, thepresent invention facilitates contaminant recovery from synthetic resinmaterials thereby enabling the contaminants to be disposed of in a safeand environmentally friendly manner.

The upstream portion of the process comprises a liquid solvent cleaningsystem 10. Solvent cleaning system generally includes three separatecleaning stages 12, 14, and 16. Particulate synthetic resin material(illustrated as feed stream 18) is initially loaded into the first stage12 which contains a liquid solvent. After a first cleaning cycle duringwhich the particulate material is vigorously mixed with the solvent, theparticulate material (illustrated as stream 20) is transferred to asecond stage 14. Stage 14 operates in a very similar manner to stage 12in that the particulate material is mixed with additional quantities ofsolvent. After the second cleaning cycle, the particulate material(illustrated as stream 22) is transferred to a third cleaning stage 16.The third stage 16 also is similar in operation to the first two stages12, 14. However, for reasons explained in greater detail below, thisstage preferably employs a greater quantity of solvent than either ofthe first two stages. Also, the solvent purity preferably increases fromstage 12 to stage 14 to stage 16. The solvent contained in eachsuccessive stage is preferably cleaner than the previous stage in orderto achieve the maximum salvation of the contaminants present on thesynthetic resin material.

It will be appreciated that the stages 12, 14, and 16 do not necessarilyneed to be carried out in separate vessels. It is believed that theoverall process functions most efficiently when these stages are carriedout in separate vessels arranged in series, as a nearly continuousprocess can be achieved. However, it is possible that fewer than threeseparate vessels could be used and instead of the resin material beingtransferred from tank to tank, different batches of solvent (havingdifferent purities) may be moved in and out of the tank during eachstage. In such manner, the particulate synthetic resin material is stillcontacted by three different batches of solvent, but need not leave theconfines of a single vessel.

The particulate material (illustrated as stream 24) is then sent to asolvent separation and recycle station 26. At station 26, a substantialportion of the solvent is separated from the particulate material andrecycled to the third cleaning stage 16 via conduit 28. Station 26preferably employs a device, such as a spin dryer, to mechanicallyseparate the solvent from the particulate material. The particulatematerial is then sent to a silo 30 via stream 32 to await furtherprocessing.

The downstream portion of the process comprises a carbon dioxidecleaning system 34. The setup of system 34 is nearly the same as thatdisclosed in U.S. Pat. No. 5,711,820, which is incorporated by referenceherein. The objective of carbon dioxide system 34 in the context of thepresent invention is slightly different than in the '820 patent. In thepresent process, a substantial portion, and preferably almost all, ofthe contaminants are removed from the synthetic resin material prior toreaching carbon dioxide system 34. However, what remains on thesynthetic resin material, in addition to trace amounts of contaminants,is mainly solvent from solvent cleaning system 10. At this stage, thesynthetic resin flakes may still comprise between 0.1-5% by weightsolvent which must be removed. Carbon dioxide system 34 is used toremove this solvent that is left over from solvent cleaning system 10.Unlike the process shown in the '820 patent, the present carbon dioxidesystem 34 is not principally directed toward removing oil contaminantsfrom the synthetic resin flakes, but instead is directed toward removingresidual solvent from the earlier system. Small amounts of contaminantsmay still be removed from the flakes during operation of carbon dioxidesystem 34, however, this is an incidental benefit as the vast majorityof the contaminants have already been removed during the solventcleaning system 10.

Preferably, the solvent used in solvent cleaning system 10 is relativelysoluble in liquid or supercritical carbon dioxide (more so than thecontaminants being removed from the synthetic resin material in system10). Therefore, one advantage of the present system is that carbondioxide system 34 can operate at lower pressures than if carbon dioxidesystem 34 were directly solvating the contaminants. Operation at lowerpressures tremendously lowers equipment costs and energy costsassociated with liquefying the carbon dioxide.

As indicated by the dashed line, system 10 is preferably a closed systememploying vessels that are sealed or blanketed with an inert gas such asnitrogen to prevent volatilization and escape of solvent to the outsideenvironment. In addition, silo 30 is preferably a closed vessel and doesnot permit much if any residual solvent adhered to the synthetic resinparticles to escape to the environment. As a closed system, system 10does not present significant environmental concerns as it is relativelyself-contained and does not produce significant emissions. Also, theclosed nature of system 10 allows for recycling of a substantial portionof the liquid solvent used therein with low make up demands. Thesefeatures result in a reduction in operating costs of approximately 40%compared to conventional water-based contaminant removal systems andalso avoids having to deal with the clean up of contaminated water.

Turning now to FIG. 2, the solvent cleaning system 10 is shown ingreater detail. Stages 12, 14 and 16 are relatively similar with thepossible exception of equipment sizing. Therefore, those features commonto all three stages are described using the same reference numerals. Afeed stream 18 of particulate material ground into approximately ⅜″flakes enters stage 12 and is directed initially to a separator 36primarily for separation of unacceptably large particles of syntheticresin material that could be difficult to process. The separator can beany sieve or filter-type apparatus suitable for performing thisseparation, however, apparatus such as a Sweco separator is preferred.The rejected particles exit separator 36 through stream 38 and may bereturned to a shredding or grinding device (not shown) for furtherprocessing to reach an acceptable size (approximately ⅜″).

Synthetic resin particles of acceptable size exit separator 36 throughstream 40 and are directed toward a conveyer 42 for distribution toeither of cleaning tanks 44 or 46. Conveyer 42 comprises a reversibleauger 48 that is capable of directing the particulate synthetic resinmaterial to both tanks 44 and 46. In operation, material is loaded intoone tank until its capacity has been reached. The cleaning cycle isbegun in that tank and auger 48 reverses direction so as to beginfilling the other tank. By providing two tanks in parallel, a nearlycontinuous process may be achieved.

Tanks 44 and 46 (and all such related tanks) are preferablydouble-walled tanks, the inner compartments 49 of which contain a liquidsolvent capable of dissolving contaminants that may be present on thesynthetic resin material. This double-wall feature provides extraprotection against accidental release of solvent and contaminants.

A feature unique to tanks 44 and 46 is that these tanks are equipped forseparation of less dense synthetic resin material from more densematerial. For example, many synthetic resin material containers madefrom polyethylene terephthalate (PET) employ caps made from less densepolypropylene material. It is often desirable to separate these twokinds of materials during recycling operations. Manual separation ofthese different materials can be very costly. The present inventionaccomplishes this separation through the careful selection of a solventthat has a specific gravity in between the specific gravities of the twokinds of materials. Therefore, the less dense polypropylene materialwill float in the solvent while the more dense PET tends to sink. Askimming device may be used to remove the lesser dense material fromtanks 44 and 46 via streams 52 and 54, respectively. Alternatively,gates located proximate the top of tanks 44 and 46 open thereby drainingthe lesser dense material along with a quantity of solvent which is thenfiltered and the solvent returned to the respective tank. In someinstances, the desired synthetic resin material may have a density thatis too close to that of the cap material to facilitate floatationseparation. It is then desirable to separate the caps from thecontainers prior to grinding of the containers.

Each of tanks 44 and 46 is equipped with a mixer 50 for agitating thecontents of the tank. Preferably, this agitation is quite significantand can be characterized as violent so as to insure the maximum possiblecontact of the synthetic resin material with the solvent. A preferredmixer 50 for use with the present system is a Neptune mixer having atleast one propeller attached to the mixer shaft.

As previously stated, tanks 44 and 46 are jacketed. The outercompartment 56 of each tank contains a heat transfer fluid for heatingand maintaining the temperature of the solvent within the innercompartment 49. Preferably, any suitable heat transfer fluid may beused, however, a glycol such as propylene glycol or ethylene glycol isparticularly preferred. The heat transfer fluid is preferably heated toa temperature of between about 170-190° F. using heat exchanger 58.Consequently, the solvent contained within the inner compartment 49 willalso be heated to a temperature between about 170-190° F. Using ajacketed vessel to heat the solvent allows heating to be accomplishedwithout use of an open flame near the solvent vessel. This feature addsto the overall safety of the system. The glycol solution is constantlycirculated between tanks 44 and 46 and heat exchanger 50 via conduits60, 62, 64, and 68.

In alternative embodiments, the solvent is not heated to such a hightemperature. For example, the solvent can be heated in the range of 90to 110° F. In one specific embodiment, the solvent is heated toapproximately 100° F. The lower temperatures help reduce operating costsand reduce the amount of solvent loss due to evaporation.

The synthetic resin particles and solvent are agitated for apredetermined length of time. This length of time is dependant upon manyfactors such as tank size, solvent purity, and the nature of the solventitself and its capacity for solubilizing the particular contaminants.However, it is preferable for agitation to occur over a relatively shorttime period, preferably less than 15 minutes, more preferably between1-12 minutes, and most preferably between about 4-5 minutes. At the endof the agitation cycle, the contents of either tank 44 or 46 are emptiedvia conduit 70 or 72, respectively. The slurry comprising solvent andsynthetic resin material is then pumped by pump 74 and directed to stage14 via conduit 76.

The slurry passes through a second separator 36 whereby the particulatematerial is separated from the solvent which is then recycled back tostage 12 via conduit 78. Pump 80 directs the recycled solvent to eithertank 44 or 46 via conduits 82 or 84, respectively. The synthetic resinmaterial (illustrated as stream 86) is directed to a second conveyer 42which distributes the particulate material between tanks 44 b and 46 b.Stage 14 then operates in a similar manner to stage 12 with theexception of the extra step of separating synthetic resin materials ofdifferent densities by flotation removal.

At the completion of the agitation cycle, the slurry of solvent andparticulate material exits the respective tank through conduit 88 or 90and is pumped by pump 92 to stage 16 via conduit 94. Stage 16 beginswith the slurry being passed through a third separator 36 with thesolvent being separated and recycled back to stage 14 through conduit96. Pump 98 directs the recycled solvent back to the appropriate tankthrough either conduit 100 or 102.

The synthetic resin material leaves separator 36 as stream 104 and isdirected to conveyer 42 for distribution between tanks 44 c and 46 c.Stage 16 then operates in a manner that is similar to the operation ofstages 12 and 14. At the completion of the agitation cycle, the solventand synthetic resin material slurry exits tanks 44 c and 46 c viaconduits 106 and 108, respectively, and is pumped by pump 110 to hydrocyclone 112 via conduit 114.

The hydro cyclone 112 separates solid waste material present in theslurry from the particulate synthetic resin material. The solid wastecould be any undesirable particulate material present in the slurryincluding metal particles and other heavy solid particles thatheretofore may have not been separated from the synthetic resin materialor solvent. This waste then exits the system as stream 116. The ratio ofsolvent to synthetic resin material present in the slurry entering thehydro cyclone is dependent upon a number of factors such as the densityof the synthetic resin material. Furthermore, the interior of the hydrocyclone must be changed out depending upon the different types ofsynthetic resin material present in the slurry.

The slurry is directed through conduit 118 toward spin dryer 120 where asubstantial portion of the solvent is separated from the synthetic resinmaterial and recycled back to stage 16 through conduit 122 and pump 124.The recycled solvent is then distributed between tanks 44 c and 46 cthrough conduits 126 and 128. Spin dryer 120 preferably removes at leastabout 90% by weight of the solvent present in the slurry, morepreferably at least about 95% by weight of the solvent, and mostpreferably at least about 98% by weight of the solvent. After exitingthe spin dryer, the particulate synthetic resin material is transportedas stream 130 to storage silo 30 where it is held until it can be sentto carbon dioxide system 34.

The solvent used in system 10 is carefully selected based on variousdesirable characteristics. First, the solvent should be capable ofsolvating a number of different kinds of contaminants without causingsignificant break down of the synthetic resin materials dispersedtherein. Second, the solvent should exhibit a specific gravity tofacilitate flotation separation of synthetic resin materials ofdifferent densities. Using the polypropylene cap and PET containerexample, it is desirable to separate the cap material from the morevaluable PET. The polypropylene material exhibits a specific gravity ofabout 0.90 whereas PET generally exhibits a specific gravity of betweenabout 1.3-1.4. Preferably, the solvent will have a specific gravity inbetween these two figures and more preferably will have a specificgravity proximate to that of water. If flotation separation is not acritical feature of the particular process, the specific gravity of thesolvent is not as critical a factor. However, it is preferable for thesolvent to comprise an organic solvent other than carbon dioxide havinga specific gravity (preferably at 20° C.) of at least about 0.76, morepreferably between about 0.9-1.5, and most preferably between about0.95-1.25. Suitable solvents may be selected from various classes ofchemicals such as esters, ketones, glycols, glycol ethers, halogenatedsolvents, aromatics, alcohols, aliphatic hydrocarbons, amines, andterpenes. More specifically, the solvent is selected from the groupconsisting of amyl propionate, butyl butyrate, alkyl lactates, ethylhexyl acetate, dibasic esters, methyl soyate, ethyl soyate,cyclohexanone, methyl ethyl ketone, dipropylene glycol, dipropyleneglycol methyl ether, trichloroethylene, xylene, ethanol,tetrahydrofurfuryl alcohol, hexane, mineral spirits, monoethanolamine,d-limonene, dimethyl formamide, n-methyl pyrrolidone, propylenecarbonate, and combinations thereof. Preferably, the solvent is an alkylester solvent having the general formula RCOOR′, wherein R and R′ areindependently selected from C1-C10 alkyl groups and R contains at leastone hydroxyl group. Alkyl lactates are particularly preferred solventsfor use with the present invention.

Preferred alkyl lactates include methyl lactate, ethyl lactate,isopropyl lactate, and butyl lactate, all of which are available underthe name PURASOLV by PURAC America, Inc., Lincolnshire, Ill. Of thealkyl lactates, ethyl lactate is particularly preferred. These solventsexhibit specific gravities at 20° C. of between 0.98-1.09, are generallymiscible with water, and have a high capacity for solvating variousorganic contaminants such as grease and oil. Furthermore, these solventsare relatively non-toxic and, in some instances, have been approved bythe FDA for food applications. The lack of solvent toxicity is an addedbenefit and contributes to the environmentally friendly nature of thissystem.

Solvent compatibility with the synthetic resin material is also animportant property as it is undesirable for the solvent to solvate thesynthetic resin material in addition to the contaminants. Syntheticresin material such as polypropylene, polyethylene, polyethyleneterephthalate, nylon, polytetrafluoroethylene, polytetrafluoroethylene,polyvinylidene fluoride, polycarbonate, fluorinated ethylene propylene,polybutylene terephthalate, polyimide, polyetherketone, polyetherimide,polybutylene, polyphenylene oxide, polystryene, polysulfone,polyethersulfone, polymethylpentene, polyvinyl chloride, acetal,acrylic, acrylonitrile-butadiene-styrene (ABS), and combinationsthereof, are considered to be compatible with many of the preferredsolvents according to the present invention.

Carbon dioxide system 34, as shown in FIG. 1, is an exemplary closedloop separation system suitable for separation of residual solventadhered to the synthetic resin particles after treatment in solventsystem 12. Carbon dioxide system 34 is also capable of removing traceamounts of contaminants that may still be present on the synthetic resinparticles; however, the primary function of system 34 is to separate thesolvent residue from the particles thereby producing solvent andcontaminant free material.

The particulate synthetic resin material is transferred from storagesilo 30 to extraction vessel 132 via stream 134 (preferably an augertransport device). Typically, the material will be enclosed in a steelmesh basket or other porous metal enclosure so that the synthetic resinmaterial will not be swept out of the extraction vessel 132 into otherportions of the separation system 34 by the flowing carbon dioxidedescribed below. The system is then filled with carbon dioxide from areservoir 136 through a control valve 138 to a pressure suitable tosatisfy the desired pressure and temperature conditions in operation asdescribed further below. With the control valves 138 and 140 shut off,carbon dioxide flow is established from the compressor 142 andassociated heat exchanger 144 through control valve 146, through theextraction vessel 132, through the expansion device 148 and associatedheat exchanger 150, through separation vessel 152 and to the compressor142 for another cycle. Adjustments to the compressor 142 speed,expansion device 148, and the temperature of the heat exchangers 144 and150 allows the extraction vessel 132 and separation vessel 152 to bemaintained at the desired pressures and temperatures as describedfurther below. Such adjustments may be made manually or controlled bycommercially-available computer software and equipment. Overall chargeof the system may be adjusted by admitting more carbon dioxide fromreservoir 136 through control valve 138 or by discharging carbon dioxideto the reservoir through control valve 140.

In the extraction vessel 132, the desired temperature and pressure forsolvency of the solvent in liquid or supercritical carbon dioxide istypically from about 600-5000 psia (more preferably from 650-1000 psia,and most preferably from about 700-800 psia) and from about 20-100° C.(more preferably from about 30-90° C., and most preferably from about60-70° C.). The solvent-free liquid or supercritical carbon dioxidecontinuously enters the bottom of the extraction vessel 132 and flowsupward past the synthetic resin material 154, dissolving the solventcarried on the material 154 (from system 10) and flushing it away. It isof some importance that the flow of carbon dioxide be introduced to thebottom of extraction vessel 132, since the upward flow will tend tofluidize the bed of synthetic resin material 154 and hasten dissolutionof the solvent.

The solvent-laden carbon dioxide continuously exits from the top ofextraction vessel 132 and flows to the expansion device 148 and heatexchanger 150. Expansion device 148 and heat exchanger 150 are set suchthat the carbon dioxide entering the separator vessel 152 is in thegaseous phase; typically from about 400-1000 psia and from about 20-35°C. Under these gaseous conditions, the carbon dioxide has negligiblesolubility for the solvent, and therefore the solvent (including anytrace amounts of contaminants) is precipitated out of solution, forminga two-phase system of liquid solvent and gaseous carbon dioxide, and thesolvent collects in the bottom of separator vessel 152. The nowsolvent-free carbon dioxide gas is compressed through the compressor 142wherein the pressure is raised equal to or greater than that of theextraction vessel 132. The temperature of the carbon dioxide then isadjusted to the desired value as it flows through heat exchanger 144,from where it reenters the extraction vessel 132 as either liquid orsupercritical (depending on the pressure and temperature chosen) carbondioxide to again dissolve and flush away solvent from the syntheticresin material 154. This recirculation of the carbon dioxide iscontinued until all of the solvent has been removed from the syntheticresin material and deposited in the separator vessel 152.

When the separation of the solvent from the synthetic resin material iscomplete, with control valve 146 closed, the clean carbon dioxide isrouted into the storage reservoir 136 through control valve 140 to beused again later. The solvent-free synthetic resin material 154 isremoved from the extraction vessel 132 (preferably by a vacuum system)and sent to a storage silo. The solvent 156 recovered is drained fromthe separator vessel 152. The only waste released by this process is thesmall amount of carbon dioxide gas vented during final depressurizationof the extraction vessel 132.

The solvent 156 recovered by carbon dioxide system 34 is preferablyrecycled to solvent cleaning system 10, or if necessary, may be sent toa purification system. Periodically, the solvent used in stages 12, 14,and 16 will need to be changed out and purified as the solvent becomessaturated with contaminants. The time period between these change outsis dependent upon a number of factors including the stage in which thesolvent is being used and the solvent's capacity or solvating power(sometime referred to as the Kauri butanol value), but is typicallyevery several hours. The solvent is drained from the respective stageand sent to a distillation system for separation of the solvent and thecontaminants. The operating conditions of the distillation system dependlargely upon the flash point of the solvent, but preferred solventsaccording to the present invention are typically heated to about 300° F.and then re-condensed. The contaminant waste is then properly disposedor recycled. Recovery of the contaminant waste for proper disposal is animportant advantage of the present invention. If the contaminants werenot recovered, particularly the more toxic contaminants, they wouldlikely wind up in a landfill along with the synthetic resin materialwhere they could cause soil and groundwater contamination.

The solvent stages 12, 14, and 16 need not be taken off-line forsubstantial periods of time during this process as fresh solvent can beadded immediately following removal of the “dirty solvent” and theprocess continued while the dirty solvent is being purified. System 10as shown in FIG. 2 is particularly designed to avoid this downtime astanks 44 and 46 are situated in parallel, so that one tank isoperational while the other is taken down for solvent change over. Inessence, the system 10 is designed to function as a continuous-batchprocess.

The aforementioned upstream liquid solvent wash system 10 and downstreamcarbon dioxide wash system 34 is well suited for implementation in aresin recycling method that produces essentially contaminant-freesynthetic resin material in an environmentally safe and economicalmanner. In general, the method includes receiving and sorting the resin.Once the resin has been sorted, it is ground into particles. Theparticles are then exposed to a solvent, the solvent contacting theresin particles and substantially removing contaminants on the resinparticles. After separating the particles and the resin, a solventremoving agent is used to remove any residual solvent remaining on theresin particles after separation. The substantially contamination-freeparticles are then sorted by type. In various embodiments, the resin isreceived in bales and initially sorted by color before grinding. Thesolvent is an organic solvent and the solvent removing agent is either aliquid or supercritical carbon. In the final sorting, thecontamination-free particles are separated by type, such as HDPE, PET,PVC, etc.

Referring to FIG. 3, a diagram illustrating a resin recycling method andapparatus according to the present invention is shown. The recyclingsystem 300 includes one or more bale breakers 302, one or more trommels304, one or more sorters 306, one or more grinders 308, one or more airclassifiers 310, one or more silos 312, the multi-tank solvent washsystem 10, hydro cyclone 112, spin dryer 120, silo 30, loader 314, oneor more carbon dioxide wash systems (34 a, 34 b, and 34 c), an airaspirator 316, silo 318, an optical sorter 320, infrared sorter 321, anda pelletizer 322.

It should be noted that for the sake of simplicity, only one recyclingline including solvent wash system 10, hydro cyclone 112, spin dryer120, silo 30, loader 314, one or more carbon dioxide wash systems (34 a,34 b, and 34 c), an air aspirator 316, silo 318, an optical sorter 320,and infrared sorter 321 is shown in the figure only for clear plasticresin. In an actual implementation of the present invention, either thenon-clear (i.e., green) resin would be separated. When a sufficientamount of the non-clear resin was collected, it would be run through theresin recycling method and apparatus as shown in FIG. 3. Alternatively,a parallel recycling line including multi-tank solvent wash system 10,hydro cyclone 112, spin dryer 120, silo 30, loader 314, one or morecarbon dioxide wash systems (34 a, 34 b, and 34 c), an air aspirator316, silo 318, an optical sorter 320, infrared sorter 321, and apelletizer 322 would be provided for the sorted green plastic resin.

it should be noted that the number of tanks in the solvent wash systemand the number of carbon dioxide systems 34 is arbitrary and is selectedbased on the desired throughput of the system. The numbers of tanks andcarbon dioxide systems illustrated and described herein should in no waybe construed as limiting the invention. Either more or fewer solventwash tanks and carbon dioxide systems may be used.

The bale breaker 302 is designed to remove the retaining wires or cablesbinding bales of compressed containers. As the bales are received, thebale breaker removes the wires holding the bale together and thenforwards the bale to the trommel 304. In the trommel 304, the compressedcontainers are repeatedly lifted, rotated and dropped in a tumblingaction, causing the individual containers to separate upon impact. Debrisuch as bottle caps and dirt are loosened by the tumbling action andtypically fall to the wayside. As the containers are tumbled in thetrommel 304, they eventually separate and are forwarded onto a conveyorbelt (not shown) and are then fed to the optical sorters 306. In oneembodiment, the optical sorter 306 separates the individual containersby color. In the example shown, into a clear stream and a green stream.The containers of the two streams are then fed into two grinders 308respectively. Each grinder 308 is designed to reduce the containers intoapproximately ⅜ inch flake shaped resin particles of like color. Thegrinders 308 are heavy duty industrial type that include a large numberof blades that grind the containers into the particles in a grindingchamber. Silos 312 are used to store the clear and green resin particlesrespectively.

The resin particles are next introduced into multi-tank solvent washsystem 10 from the silo 312. As described in detail above, the particlesare exposed to a solvent in the tanks, thereby substantially removingcontaminants on the particles. The hydro cyclone 112 separates the solidwaste material present in the slurry exiting the solvent wash system 10and the spin dryer 120 is used to separate the solvent from the resinparticles. The particles are then stored in another silo 30 before beingloaded by loader 314 into the carbon dioxide wash systems 34 a, 34 b,and 34 c. The air aspirator 316 separates any bits of label paper orother light material present on the substantially solvent-free resinexisting the carbon dioxide wash. The optical sorter 320 is used toseparate the resin stored in silo 318 by type, for example HDPE, PET,PVC, mixed plastic, vinyl chloride, polyethylense, etc. Infrared sorter321 sorts by color. In an optional step, the sorted resin particles maybe pelletized by pelletizer 322. Once the particles have been sorted bytype and optionally pelletized, the material can be recycled and reusedto make packaging containers and bottles.

With the above describe system and method, the sorting of the plasticresin is purposely done at different stages of the process. Thisredundancy helps assure that the final product is sorted by resin typeand color to a very high degree of accuracy. As a general rule of thumb,the bales as received are typically “pre-sorted” That is, the balesgenerally contain one type of plastic resin, such as either PET or HDPE.The problem with the bales, however, is that containers in the bales aretypically pre-sorted by humans. The bales consequently often containcontainers of a resin type that does not belong in the bale due to humanerror. The optical sorter 306 performs a first sorting by color. Theresin sorted by color then travels through separate solvent wash andcarbon dioxide wash lines as described above. Sorting is also performedwithin the multi-tank solvent wash system 10. As noted above, byselecting the specific gravity of the solvent, high density resin can besorted or separated from low density materials. For example, manysynthetic resin material containers made from polyethylene terephthalate(PET) employ caps made from less dense polypropylene material. It isoften desirable to separate these two kinds of materials duringrecycling operations. The less dense polypropylene material may beskimmed from the top of the solvent tanks and collected. When asufficient amount of the polypropylene material is collected, it too maybe passed through the system shown in FIG. 3. Sorting is also performedat the back end of the system and method. The optical sorter 320 sortsby the type of resin, such as HDPE, PET, PVC, mixed plastic, vinylchloride, polyethylense, etc. An optional sorter 321 also sorts bycolor. By building sorting redundancy into the system, the final productcan be sorted to a very high degree of accuracy.

The aforementioned system is also designed to remove any paper labelsand similar contaminants provided on the bottles and containers receivedon the bales. Paper labels are typically attached to bottles andcontainers by glue on the edges of the label. During grinding in thegrinders 308, the non-glued portion of the labels on the containers aretypically liberated. The ground resin particles are next passed throughair classifiers 310. Using an adjustable airflow and baffles, theclassifiers 310 blow or remove fines and light fragments, such as theliberated labels, from the resin particles. In the multi-tank solventwash system 10, the glue used to attach labels onto the resin particlesis typically dissolved and remove, liberating any remaining portion ofthe labels affixed to the resin by the glue. Finally, the air aspirator316 removes any remaining bits and pieces of labels, other fines orlight fragments not removed by either hydrocyclone 112 or the spin dryer120. As a result, labels or other fines are substantially removed fromthe resin particles stored in silo 320.

The solvent recycle station 26 includes, in one embodiment, a dirtysolvent tank 330, a solvent still 322 and a clean solvent tank 334.During recycling operations, the solvent in the multi-tank system 10becomes dirty from the contaminants removed from the resin particles.When the solvent needs to be replaced, it is removed from the multi-tanksolvent wash system 10 and stored in the dirty solvent tank 330. Cleansolvent is then removed from the clean solvent tank 334 to replenish theremoved solvent from the tanks. The dirty solvent is pumped into solventstill 332 while pulling a vacuum at a very high temperature (e.g. 250 to350 degrees F., and in one specific embodiment 300 degrees F.), causingthe dirty solvent to convert into a gaseous state. The contaminants,however, remain in the solid state and drop into a collect bucket in thesolvent still. The cleaned solvent is then cooled back to the liquidstate in coils and then stored in the clean solvent tank 334 for lateruse.

The pellitizer 322 is a machine that converts the cleaned resinparticles, typically in flake form, into pellets. The pellitizer heatsthe resin particles from a solid state into a liquid state. The liquidis then pushed or extruded through a filter screen and die plate. Thefilter screen removes any particles or contaminants in the liquid resin.As the liquid is extruded through the die plate, knife blades cut theresin, forming pellets upon solidification.

In the beverage industry for example, the bottles are often made fromvirgin PET material in pellet form. With the present invention, therecycled resin in pellet form is sufficiently clean and free ofcontaminants, residue, or odors that it can readily meet or exceed thehigh qualification standards required by most bottlers. Thus with thesystem and system for the present invention, the bottles can be made forthe soda and beverage industry using completely recycled resin, or a mixof recycled and virgin resin.

Although the invention has been described with reference to theembodiments illustrated in the attached drawing figures, it is notedthat equivalents may be employed and substitutions made herein withoutdeparting from the scope of the invention as recited in the claims. Forexample, the sorting can occur using some other criteria besides thecolor or the containers or the type of material. The size in which theresin particles are ground is also optional and can be made eitherlarger or smaller than specified herein. The type of solvent or thesolvent removing agent used is also arbitrary and does not necessarilyhave to be of the same type or phase described herein. Having thusdescribed the various embodiment of the invention, what is claimed asnew and desired to be protected by Letters Patent includes thefollowing:

1. A system for recycling resin, comprising: one or more solvent washvessels to expose resin particles to a solvent, the solvent contactingthe resin particles in the one or more solvent wash vessels tosubstantially remove contaminants on the resin particles; a separator toseparate the solvent from the resin particles after removal from the oneor more solvent wash vessels, the separator including a hydro cyclonefollowed by a spin dryer, the separator resulting in the removal of atleast 90 percent by weight of the solvent from the resin particles; anda solvent removing element to expose the resin particles to a solventremoving environment containing either liquid or supercritical carbondioxide maintained at a predetermined temperature and pressure withinthe solvent removing element is the solvent removing environmentconducive to substantially remove residual solvent remaining on theresin particles after separation.
 2. The system of claim 1, wherein theone or more solvent wash vessels further include one or more agitatorsto agitate the resin particles in the solvent for a predetermined periodof time in the one or more solvent wash vessels respectively.
 3. Thesystem of claim 2, wherein the predetermined period of time consists ofone of the following: less than 15 minutes; between 1 to 12 minutes; orbetween 4 to 5 minutes.
 4. The system of claim 1, wherein the one ormore solvent wash vessels further comprises one or more heating elementsto heat the solvent to a predetermined temperature while contacting theresin particles in the one or more solvent wash vessels respectively. 5.The system of claim 4, wherein the predetermined temperature consists ofone of the following: a range from 170 to 190 degrees Fahrenheit a rangeof 90 to 110 degrees Fahrenheit; or approximately 100 degreesFahrenheit.
 6. The system of claim 1, wherein the one or more solventwash vessels includes a first solvent wash vessel to expose the resinparticles to the solvent in a first solvent wash using a first solventhaving a first purity.
 7. The system of claim 6, wherein the one or moresolvent wash vessels includes a second solvent wash vessel to expose theresin particles to the solvent in a second solvent wash using a secondsolvent having a second purity.
 8. The system of claim 7, wherein theone or more solvent wash vessels includes a third solvent wash vessel toexpose the resin particles to a third solvent wash using a third solventhaving a third purity.
 9. The system of claim 8, wherein the resinparticles are transported between the first solvent wash vessel, thesecond solvent wash vessel, and the third solvent vessel so that theresin particles are exposed to the first solvent of the first impurity,the second solvent of the second impurity, and the third solvent of thethird impurity consecutively.
 10. The system of claim 8, wherein thefirst purity is less than the second purity, which is less than thethird purity.
 11. The system of claim 1, wherein the one or more solventwash vessels includes a single solvent wash vessel wherein a firstsolvent wash, a second solvent wash are successively performed in thesingle solvent wash vessel.
 12. The system of claim 1, wherein thesolvent used in the one or more solvent wash vessels is configured tosubstantially not break down the resin particles while removing thecontaminants from the resin particles.
 13. The system of claim 1,wherein, in the one or more solvent wash vessels, the solvent isconfigured to solvate one or more of the following types of contaminantsfrom the resin particles: oil; milk, soda; pesticides; detergents; or acombination thereof.
 14. The system of claim 1, wherein the solvent hasa predetermined specific gravity to facilitate the separation of theresin particles by density.
 15. The system of claim 14, wherein thepredetermined specific gravity consists of one of the following: atleast 0.87; between 0.9-1.5; or 0.95-1.25.
 16. The system of claim 1,wherein the solvent is an organic solvent.
 17. The system of claim 1wherein the solvent is selected from the group consisting of amylpropionate, butyl butyrate, alkyl lactates, ethyl hexyl acetate, dibasicesters, methyl soyate, ethyl soyate, cyclohexanone, methyl ethyl ketone,dipropylene glycol, dipropylene glycol methyl ether, trichloroethylene,xylene, ethanol, tetrahydrofurluryl, hexane, mineral spirits,monoethanolamine, d-limonene, dimethyl formamide, n-methyl pyrrolodine,propylene carbonate, and combinations thereof, and wherein said alkyllactate is selected from the group consisting of methyl lactate, ethyllactate, isopropyl lactate, butyl lactate and combinations thereof. 18.The system of claim 1, wherein the solvent is an alkyl ester solventhaving the general formula RCOOR′, wherein R and R′ are independentlyselected from C1-C10 alkyl groups and R contains at least one hydroxylgroup.
 19. The system of claim 1, wherein the resin particles areselected from the group consisting of polypropylene, polyethylene,polyethylene terephthalate, nylon, teflon, polytetrafluoroethylene,polyvinylidene fluoride, and combinations thereof.
 20. The system ofclaim 1, further comprising an aspirator to remove bits of label paperfrom the resin particles.
 21. The system of claim 1, further comprisinga receiving location configured to receive the resin in the form ofcompacted bales of resin containers, the receiving location furtherincluding a bale breaker configured to remove any binding element usedto hold the bales together.
 22. The system of claim 21, furthercomprising a trommel to substantially separate the containers of thebales.
 23. The system of claim 1, further comprising a first sorter tosort the resin by color.
 24. The system of claim 23, wherein the firstsorter is configured to sort the resin into clear resin and coloredresin.
 25. The system of claim 23, wherein the first sorter is anoptical sorter.
 26. The system of claim 1, further comprising a grinderconfigured to grind the resin into the resin particles prior to exposingthe resin particles to the solvent.
 27. The system of claim 1, furthercomprising a second sorter to sort the resin particles by type, thetypes consisting of one or more of the following: HDPE, PET, PVC, mixedplastic, vinyl chloride, polyethylense.
 28. the system of claim 27,wherein the second sorter is an optical sorter.
 29. The system of claim1, further comprising a pelletizer to pellitize the resin particlesafter substantially removing the solvent in the solvent removingelement.
 30. The system of claim 1, wherein the resin particles areflakes.
 31. The system of claim 30, wherein the flakes are approximately⅜ inch flakes.
 32. A method for removing contaminants from syntheticresin material comprising: contacting particulate synthetic resinmaterial containing at least one contaminant with an alkyl lactatesolvent in a vessel, at least a portion of said at least one contaminantbeing removed from said particulate synthetic resin material andbecoming dissolved in said solvent; removing said particulate syntheticresin material from said solvent; introducing said particulate syntheticresin material into a dryer; drying said particulate synthetic resinmaterial by removing at least a portion of said solvent remaining on theparticulate synthetic resin material in said dryer; and agitating thedried synthetic resin material in an extraction vessel containing eitherliquid or supercritical carbon dioxide, the agitation of the syntheticresin material in the liquid or supercritical carbon dioxide resultingin the removal of substantially any remaining solvent or contaminantremaining of the synthetic resin material after drying.
 33. The methodof claim 32, wherein said synthetic resin material is selected from thegroup consisting of polypropylene, polyethylene, polyethyleneterephthalate, nylon, polytetrafluoroethylene, polytetrafluoroethylene,polyvinylidene fluoride, polycarbonate, fluorinated ethylene propylene,polybutylene terephthalate, polyimide, polyetherketone, polyetherimide,polybutylene, polyphenylene oxide, polystyrene, polysulfone,polyethersulfone, polymethethylpentene, polyvinyl chloride, acetal,acrylic, ABS, and combinations thereof.
 34. The method of claim 32,wherein said alkyl lactate is selected from the group consisting ofmethyl lactate, ethyl lactate, isopropyl lactate, butyl lactate andcombinations thereof.
 35. The method of claim 32, wherein saidcontacting step comprises agitating said particulate synthetic resinmaterial in said solvent.
 36. The method of claim 35 further comprisingheating said solvent when contacting said particulate synthetic resinmaterial in said solvent.
 37. The method of claim 32, further comprisingpassing said particulate synthetic resin material through a hydrocyclone prior to performing the steps of introducing said particulatesynthetic resin material into said dryer and drying said particulatesynthetic resin material.
 38. The method of claim 32, wherein saidparticulate synthetic resin material comprises particles of differentdensities and said contacting step includes separating the more densesynthetic resin particles from the less dense synthetic resin particlesby floatation of said less dense synthetic resin particles in saidsolvent.
 39. The method of claim 32, further comprising spinning thesynthetic resin material in the dryer.
 40. The method of claim 32,further comprising maintaining the temperature in the dryer at a dryingtemperature.
 41. The method of claim 32, wherein drying said particulatesynthetic resin material further comprises one or more of the following:(i) removing at least 90 percent by weight of said solvent from saidparticulate synthetic resin material in said dryer; (ii) removing atleast 95 percent by weight of said solvent from said particulatesynthetic resin material in said dryer; or (iii) removing at least 98percent by weight of said solvent from the particulate synthetic resinmaterial in said dryer.